const { Duplex } = require('stream');

const inoutStream = new Duplex({
                                   write(chunk, encoding, callback) {
                                       console.log(chunk.toString());
                                       callback();
                                   },

                                   read(size) {
                                       this.push(String.fromCharCode(this.currentCharCode++));
                                       if (this.currentCharCode > 90) {
                                           this.push(null);
                                       }
                                   }
                               });

inoutStream.currentCharCode = 65;

process.stdin.pipe(inoutStream).pipe(process.stdout);